The ability to simultaneously communicate analog and digital signals through a communications channel is well known. In one such prior art technique, voice and data signals are typically transmitted via either frequency-division multiplexing or time-division multiplexing. In frequency-division multiplexing, the data channel and voice channel are allocated different sub-bands of the channel's bandwidth, as for example disclosed in U.S. Pat. Nos. 4,546,212, 4,672,602 and 4,757,495. In time-division multiplexing, voice signals are sampled, digitized, and interleaved with digital data to form a single information stream that is communicated over the available channel. Many digital carrier systems, as for example a T1 carrier system, use such time-division multiplexing. In another communications method disclosed in U.S. Pat. No. 4,512,013, a technique similar to frequency division multiplexing is used to attain simultaneous voice and data half-duplex operation. Finally, co-pending U.S. patent application Ser. No. 08/076,526, the disclosure of which is incorporated herein by reference, teaches a method for simultaneously transmitting voice and data, or either voice or data alone, through a communications channel in a non-multiplexed manner using a generally coextensive frequency band.
In each of the foregoing techniques, a modem interconnects associated telephone and data terminal equipment (DTE) to other remote telephones and data terminal equipment through a communications link that is typically part of (or otherwise connected with) the public switched telephone network (PSTN). The modem must appropriately interact with its associated telephone and DTE for incoming and outgoing calls. For incoming calls, such interaction includes providing an off-hook signal to the communications link and ringing the phone for voice calls, or appropriately forwarding the incoming data to the DTE, or a combination of both these functions. One prior art technique of providing this interaction for a communication comprising simultaneously-transmitted or coupled voice and data signals requires that the communication be established by using an applications program that activates a modem's autodialer. The users at each end of the communications link are expected to be "standing by" and, when the applications program detects or recognizes the receipt of an incoming data signal, the respective telephones are taken off hook. The obvious drawback of this procedure is that it requires that communications be pre-scheduled. In addition, the communication begins as only a data call with voice communication being subsequently added thereto.
While the foregoing methodology provides satisfactory functionality, it is not suitable for many communications users who use their voice and data communications equipment in a typically arbitrary, unscheduled, and unplanned manner. There is therefore a significant unmet need for a technique in which a modem interacts with its associated telephone or voice equipment and DTE in a manner compatible with such normal usage.